All the below measurements are in-room response. The distortion measurements are performed on-axis in the near field to mitigate any room boundary effects. The frequency response test was performed at 1-meter on-axis.

The plot above is the standard in-room frequency response test of the REL T-9 Subwoofer. This test result is remarkably flat despite the expected boundary and room-induced modal effects. The gentle low end roll off starts at around 34 Hz with strong response all the way down to 20 Hz. The upper end usable response extends to about 120 Hz. All in all, this is a very solid result for a compact sub.

The T-9 was something of an enigma, capable of clean output up to 120 dB. THD + N on this plot was less than 1%!

At a more pedestrian output level (110 dB), the distortion (THD+N) dropped to 0.39%.

Tested at 40Hz, the distortion rose significantly but was still quite acceptable at 1.77%.

The 32 Hz plot was also clean and the measured THD+N at 110 dB was just over 1.3%.

The measured THD+N at 24Hz hit approximately 10% with the level at 98 dB. Distortion rose steadily with higher SPLs and/or lower frequencies.